swift-字符和字符串

• OC定义字符：

  char charValue = 'a';

• swift定义字符：

  var charValue : Character = "a"

• Unicode 国际标准的文本编码，他几乎能够表示全部国家的字符、
  OC能够存储ASCII字符，swift能够存ASCII+Unicode

  var charValue :Character = "🐶" //正确的
   var charValue2:Character = "小玉" //正确的
   var charValue3:Character = "玉" //错误的
  
   字符串是能够存不少字符的集合。
   OC:NSString * stringValue = @"小玉";
   swift:let stringValue:String = "小玉"
  
   区别：NSString/String  @""/""
  
   //String -> NSString
   let string:NSString = NSString(string: "dahuan")
  
   OC是以‘\0’为字符串结束：NSString * stringValue = @"aaaa\0bbbb";
   swift不是以'\0'结束：let stringValue:String = "aaaa\0bbbb"

• 字符串的经常使用方法

  • 一、初始化空字符串

    let emptyString = ""
      let emptyString2 = String()

  • 二、遍历字符串

    let string2 = "康姐是咱们的好朋友！"
      for a in string2.characters {
          print(a)
      }

  • 三、获取字符串的长度

    let count = string2.characters.count
      print(count)

  • 四、判断字符串是否为空

    let emptyStr = "1"
      if emptyStr.isEmpty {
          print("yes")
      }

  • 五、字符串的拼接

    let str1 = "康姐"
      let str2 = "是咱们的好朋友！"
      let result = str1 + str2
    
      var str3 = "haha"
      str3 = str3 + str2
      print(str3)

  • 六、格式化字符串

    let intValue = 10
      let str4 = "爱情"
      let str5 = "\(intValue)、由于\(str4)，不会悲伤"
      print(str5)
    
      //取小数后两位
      let pi = 3.1415
      let str6 = String(format: "%.2f", pi)
      print(str6)

  • 七、字符串比较

    //和C语言strcmp同样
    
      let str7 = "a"
      let str8 = "ab"
    
      if str7 > str8 {
          print(">")
      } else if str7 < str8 {
          print("<")
      }

  • 八、是否有先后缀

    let str9 = "www.baidu.com"
      if str9.hasPrefix("www") {
          print("yes")
      } else {
          print("no")
      }
      if str9.hasSuffix("cm") {
          print("yes")
      } else {
          print("no")
      }

  • 九、大小写

    let str10 = str9.uppercaseString
      let str11 = str9.lowercaseString
    
      print(str10)

  • 十、String转基本数据类型

    let str12 = "5.2吗"
      let num = Float(str12)
      print(num)

  • 十一、截取字符串

    let str13 = "康姐是咱们的好朋友！"
          //str13.startIndex  从0开始 Index不是int
          let fromStr = str13.startIndex.advancedBy(2)
          let toStr = str13.endIndex.advancedBy(-2)
          let str14 = str13.substringFromIndex(toStr)
    
    
          let range:Range <String.Index> = Range(start: fromStr, end: toStr)
          let str15 = str13.substringWithRange(range)
    
          print(str15)
    
          let toStr1 = (str13 as NSString).substringToIndex(2);
          print(toStr1)
    
          let range1 = NSRange(location: 2, length: 6)
    
          let toStr2 = (str13 as NSString).substringWithRange(range1)
          print(toStr2)